Biorefineries process biological materials such as lignocellulosic biomass, or components derived therefrom, to extract and produce valuable materials. Lignin utilization is a key biorefinery concept, and efficient lignin utilization is important for improving the economic viability of biorefineries. New technologies are needed to convert polymeric lignin into high value low molecular weight and/or monomeric feedstocks, including aromatic feedstocks.
Lignocellulosic biomass is derived from agricultural wastes, forest residues and dedicated energy crops. In recent years, tremendous effort has been applied to develop methods for extraction of useful compounds from lignocellulosic biomass. However, one of the greatest limitations facing the economic viability of this technology is the recalcitrant nature of the lignocellulosic biomass, which resists breakdown and extraction of useful compounds. This resistance necessitates the use of treatment steps to enhance the accessibility to and depolymerization of the carbohydrate and lignin components present in the lignocellulosic biomass. Most treatment processes are comprised of thermo-chemical processes that utilize combinations of high temperatures and pressures, or dilute acids or alkalis, to open up the structure of the biomass. Such processes necessitate the use of specialized equipment and high-energy inputs.
Polymeric lignin may be produced in various industrial processes such as during the pulping of hard and softwoods. Generally, it is produced as a byproduct in the paper and pulp industry. Polymeric lignin includes kraft lignin, produced via the kraft process, lignosulfonates, produced, e.g. from the sulfite pulping process, alkali lignin, produced, e.g. from treating the black liquor from the soda process with acid, and low sulfonate alkali lignin. As with lignocellulosic biomass, high-value lignin compounds may be further extracted, purified, and/or derivatized from polymeric lignin.
Ionic liquids (ILs) have come into prominence over recent years and have been used as innovative fluids for chemical processing. They are known as environmentally friendly solvents primarily due to their low volatility and their potential recyclability. Recently, the use of ILs for the treatment of biomass has been shown to be a promising technology, allowing for the solubilization of crystalline cellulose from biomass under relatively mild conditions.
The ionic liquid treatment process can generally be described as the dissolution of biomass into the ionic liquid at an elevated temperature with stirring, followed by the addition of a precipitant (or, alternatively, an anti-solvent) that precipitates the biomass from solution. This precipitant or anti-solvent is typically either water or ethanol, or some other solvent with hydrogen bonding capacity. Once the biomass has been precipitated, solid/liquid separation and downstream enzymatic or chemical processes of the now amorphous biomass may result in useful products.
Lignin components isolated from lignocellulosic biomass or polymeric lignin find use in many industrial processes such as the production of vanillin, flavorings and perfumes, plastics and polymers, carbon fiber, binders, adhesives, oil drilling mud, mud-sand cements, flame retardants, lime plaster, storage battery plates, nitrogenous fertilizers, gypsum wallboards, or as a dispersant, flotation agent, emulsifier, stabilizer, grinding agent, electrolytic refining agent, protein precipitant, tanning agent, crystal growth inhibitor, or as packaging material. Lignin is also a natural and renewable source for many low molecular weight chemicals like benzene, phenol, guaiacol, vanillic acid, methanol, acetic acid, DMSO, etc. Moreover, due to the high chemical energy of these lignin compounds, they can be used as fuel by directly burning, or conversion into a coal or petroleum substitute. Importantly, lignin components isolated from lignocellulosic biomass represent the only renewable source of these useful lignin-derived compounds.
Although treatment of lignocellulosic biomass with ionic liquids has met with success, ionic liquids are expensive and the treatment process is both energy and time intensive. As such, what is needed in the art is a process that employs less ionic liquid via higher loading capacity, and produces a supply of commercially useful, high-value, and renewable lignin compounds to help improve overall process economics. The present invention provides a treatment process that fulfills these and other needs.